The present invention relates to a magnetic recording medium such as a magnetic disk, a magnetic tape, a magnetic sheet and so on.
In recent years, on magnetic recording media, especially on magnetic recording media for video use on which short-wave recording is needed, high recording density and high reproducing output in short-wave-recording are required. For these requirements, ferromagnetic metal powder such as .gamma.-Fe.sub.2 O.sub.3 fine particle of a cobalt-covered type or a doping type has been used as ferromagnetic powder.
In order to obtain a magnetic recording medium having high recording density and high reproducing output in short-wave-recording, it is required to enhance surface smoothness of a magnetic layer to the utmost. As a means for meeting this requirement, temperature and pressure for a calendering process are raised as far as possible. Therefore, calender rolls are contaminated, resulting in lower production efficiency.
For coping with the foregoing, a specific functional group is contained in polyurethane in Japanese Patent Publication Open to Public Inspection No. 302929/1990 (hereinafter referred to as Japanese Patent O.P.I. Publication). However, even when this resin is used, the problem of contamination on calender rolls can not be solved completely. The reason for this is that contamination on calender rolls is not affected simply by materials composing a magnetic layer but is affected by physical properties in coating of a magnetic layer.
Further, other trouble caused by the enhanced smoothness on the surface of the magnetic recording medium is deterioration of a traveling or running property of the magnetic recording medium. When a magnetic recording medium having high smoothness on the surface of the medium is caused to travel for a long period of time, running problems may be caused by some conditions of temperature and humidity.
In order to solve this problem, a lubricant has been added to a magnetic layer. This method, however, has proved unable to overcome the following disadvantages. Namely, independently of whether a lubricant is added to a magnetic layer or not, when the magnetic layer is pressed by a magnetic head or by a guide pin, the actual contact area between them is increased, which causes a rise in friction between the medium and the head or the guide pin, resulting in a tendency of unstable running of the medium and consequent sticking and edge-folding of the medium and clogging of the magnetic head.